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Author Topic: Whatever you do dont put B's in there (6146B's) and the HW101..  (Read 17760 times)
G3RZP
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« Reply #15 on: December 01, 2015, 04:55:06 AM »

Quote
Best answer is to measure the bias needed to idle the 6146 then the 6146B.

From the RCA data sheets:

6146, plate volts 300, screen volts 200, 5.5 volts on heater, bias -33 volts, plate current 45 to 83mA

6146A, plate volts 300, screen volts 200, 6.3 volts on heater, bias -33 volts, plate current 46 to 94mA

6146B, plate volts 400, screen volts 200, 6.75 volts on heater, bias -34 volts, plate current 46 to 94mA

So a bit difficult to compare.....

The transmitters I put into production never had a problem with any of the varieties of 6146, either RCA, GE, Brimar, Mullard/Philips or the French Mazda-Belvu, although we mainly used the RCA 6146B - the others were tried to prove compatibility. The various transmitters used about 9,000 in total at two companies I worked for......
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K9AXN
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« Reply #16 on: December 01, 2015, 11:48:29 AM »

Any radio will accommodate all three tubes if it's designed with the bias and neutralizing range to support them.

What I am trying to articulate is that the cg to p value will follow the bias range of the tube.  The bias range is 2/1 as you see with 46 to 94 ma using the same parameters. 

What I'm suggesting is, you will find the 6146B prejudiced toward the high bias end and the cg to p will follow; requiring more neutralizing feedback.  It is different but not so different as to prohibit being defined the same as the 6146.

Family holiday events call --- CYA January.

Would like to wish everyone a Merry Christmas and Happy Holiday season --- this will be the last one we will see this year Grin

Kindest regards Jim K9AXN
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W1BR
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« Reply #17 on: December 02, 2015, 07:45:03 AM »

Any radio will accommodate all three tubes if it's designed with the bias and neutralizing range to support them.

 
Kindest regards Jim K9AXN

Agreed.  Some weren't designed with much latitude to compensate for small variations, however.
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KM1H
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« Reply #18 on: December 02, 2015, 09:55:26 AM »

Motorola had their own tube number and I suspect they were tested for a very narrow range of specs (such as Eimac Y tubes) as a way to force 2 way radio owners to buy them at a much inflated price. OTOH I helped a local shop at times and found the majority of 6146B's I tried were well neutralized. Some were not useable but the cost savings were substantial and I could use the rejects in ham gear.

Carl
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G3RZP
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« Reply #19 on: December 02, 2015, 01:34:27 PM »

Quote
Agreed.  Some weren't designed with much latitude to compensate for small variations, however.

Does lead me to question 'How well were they designed?'

If you look at lot of designs in ham radio magazines and try tolerancing them over the full range of device characteristics, many of them fail. The authors get very upset when this is pointed out to them....
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K4JPN
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« Reply #20 on: December 14, 2015, 08:51:41 AM »

I ran 6146B in my HW-101 for years and no problem.  I did neutralize by disconnecting the screen and plate voltage, rather then the simple way in the HW-101 manual.  I have the directions to do this in my HW-101 service bulletins.  No problems.  I have a collection of HW-101 mods at http://www.thewinstonator.com/ham_radio_2.htm these include the service bulletins and all the mods I tested and made to my HW-101.  73, Steve K4JPN
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K9AXN
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« Reply #21 on: January 07, 2016, 04:51:47 PM »

Is your HW-101neutral on all bands and if not which bands are off?

Also have you looked at change notes HW101-18   --- 39 --- 49 etc regarding the 6146B. 

Did you find the neutralizing cap needed to be adjusted for more capacity for the 6146B.

Not concerned whether it worked in the end or not, just whether it was neutral on all bands and after you installed the 6146B's quantify the difference.

Did you find you had to touch up the neutralizing adjustment after the no plate and screen voltage technique.

Appreciate your looking at this.     

Kindest regards Jim
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W5RKL
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« Reply #22 on: January 09, 2016, 06:30:53 AM »

Is your HW-101neutral on all bands and if not which bands are off?

Also have you looked at change notes HW101-18   --- 39 --- 49 etc regarding the 6146B. 

Did you find the neutralizing cap needed to be adjusted for more capacity for the 6146B.

Not concerned whether it worked in the end or not, just whether it was neutral on all bands and after you installed the 6146B's quantify the difference.

Did you find you had to touch up the neutralizing adjustment after the no plate and screen voltage technique.

Appreciate your looking at this.     

Kindest regards Jim

Read Tom Rauch, W8JI, webpage on neutralizing Grid Driven Tetrodes such as the 6146:

http://www.w8ji.com/neutralizing__amplifier.htm


73
Mike W5RKL
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K9AXN
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« Reply #23 on: January 10, 2016, 08:48:26 AM »

Hi Mike,

Tom's examples and explanations regarding neutralization for grid driven amplifiers have too many errors and lacks the depth needed to explain the reasons for the variations in behavior found in beam power tetrodes i.e. the 6146, 8122, and others.  For a comprehensive explanation for neutralizing grid driven amplifiers see  http://k9axn.com/_mgxroot/page_10873.html

The volumes that I've used for the last 57 years comprehensively explain the concept of neutralization and the reasoning behind it.  They are Electronic and Radio Engineering 4th edition Terman,  and The RCA Radiotron designers handbook Langford Smith.  Both good books but the RCA volume is disjointed and takes time to find what you're looking for and it's hard to lift.  Termans book gets the gold ring.

What I suggested is, the design of a MULTI-BAND radio uses a subset of a particular tube with a narrower range of operating values than a single band radio.  Why?  

The control grid to plate inter-electrode capacity follows the bias numbers but is exaggerated in beam power tetrodes.  That's to say the CG to P and CG to K capacity increases as the idle bias level increases.  This is caused by the misalignment of the CG and SG which must be precise in a beam tetrode.  The increased SG to K influences the idle bias and the increased CG to P the neutrality.

In a multi band radio the neutralizing bridge generally has to be tweaked for each band and will track only with a narrower subset of a specific tube type retaining all band neutrality.

That being said, I ask simply, is the HW-101 neutral on all bands using either the 6146, 6146A, or 6146B after being neutralized as per the manual or however your comfortable.  

BTW Thanks for the service notes Steve!

Neutralized to me means plate dip and max out simo, while lightly loaded.  Amplifiers that traditionally are tuned with screen current can be tested this way by loading lightly.

Kindest regards Jim  
« Last Edit: July 03, 2016, 07:19:11 PM by K9AXN » Logged
AB1MN
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Posts: 62




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« Reply #24 on: January 11, 2016, 08:04:30 AM »

Hi all,

One thing that I have noticed in the past (and probably consistent with what Jim is saying) is that for rigs like the HW-101 and SB-10x, the bridge neutralizing circuit (as commonly attributed to Bruene) is not frequency independent. By removing the plate and screen voltages on the PA circuit and applying drive, one can null the output for a given band (e.g., 15m) through adjustment of the neutralizing cap, but then find that the null is different on other bands (e.g., 20m or 10m). If the neutralizing circuit were a perfect bridge, one would expect it to be frequency independent and the neutralizing adjustment to be the same on all bands.

The neutralizing circuit works by feeding back a small amount of the RF from the plate circuit to the bottom of the grid circuit for the PA (typically, the tuned circuit is in the driver plate circuit). The bottom of the grid circuit is maintained slightly above RF ground by the value of the bypass capacitor at the bottom of the grid circuit. At resonance, the bottom of the grid circuit is 180 degrees out-of-phase with the plate circuit so the neutralizing circuit balances out the RF fed through the PA tubes by feeding by and equal amount of out-of-phase energy.

Some rigs, for example the Hallicrafters SR-400, switch in different values of bypass capacitors at the bottom of the grid circuit to attempt to maintain the bridge in balance for the different bands. This is not the case on the Heathkit design and therefore the Heathkit neutralization circuit adjustment is at best a compromise across the three main bands of interest. A common solution to the compromise is to perform the neutralization on 15 meters and hope for a reasonable balance on 20 and 10.

Note that none of this has anything to do with whether you are using 6146, 6146a or 6146b tubes, or something else in the PA circuit. If you can null out the fed-through RF using the neutralizing capacitor, then the neutralizing circuit is doing its job.

Now, coming back to Jim's comment - it is interesting to reflect on how slight differences in the internal structure of the PA tubes might affect the neutralization, particularly with regard to changes in the internal capacitance with varying bias and/or drive. This is an area where I will have to defer to Jim as he has much more knowledge in this area than do I, but it has go me thinking about considering using balanced tubes (i.e, ones that draw the same plate current for a given bias setting) as a starting point.

Interesting discussion and food for thought,

Bob  AB1MN
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